Relations of the Alloys of Platinum. 433 



enough together to fully exhibit the character of the locus be- 

 tween them. Unfortunately the body of platinum from which 

 I made my alloys was not rigorously pure, an annoyance which 

 in the course of other parts of my work I had occasion to re- 

 gret. So far as the present investigation goes, however, the 

 hurtful effect of the impure platinum body is nil. It will ap- 

 pear even more clearly below, that the law to be investigated 

 is independent of the ingredients of the platinum alloy, ex- 

 cept in so far as they modify its electrical conductivity. Al- 

 loying here is merely a means of modifying resistance, and the 

 results are studied with regard to the resistance produced, not 

 with regard to the way in which resistance is modified. 



6. In making the alloys a weighed amount of platinum was 

 fused down on a lime hearth before the oxyhydrogen flame. 

 The foreign ingredient was then added, and the product after 

 cooling rolled down and drawn to wire form. The initiated 

 will know that accidents are not infrequent and that the tedi- 

 ous operations must often be repeated. The details of fusion 

 and other manipulation are given in the Bulletin. To make 

 the electrical measurement, selected parts (length 30 cm , diame- 

 ter 0*045 cm ) of the wires were annealed at a red heat and then 

 wrapped in a single layer around a little cylinder of porcelain 

 (length 2 cm , diameter # 45 cm ) in such a way that the spires of 

 the helix did not touch. The ends were appropriately fused 

 to copper terminals. The little helix was then introduced into 

 the space of constant temperature of my boiling tube, and con- 

 secutively heated to 25°, 100° (steam), 357° (mercury vapor). 



The results of the measurements are given in the following 

 table. The series contains 57 alloys, of which J denotes the 

 density and s the zero specific resistance. The table contains 

 two values for the temperature coefficient «, the first of which, 

 «J 00 , holds for the mean increase between 0° and 100°, the 

 second between 0° and 357°, linear equations presupposed. 



The wires A, B, C, are of the same platinum body (B), pu- 

 rified by long-continued intense fusions on lime, before the 

 oxyhydrogen blow -pipe. 



The relation of these data to each other may be exhibited 

 graphically, and since «J 00 is very nearly f (o): f (o), the fol- 

 lowing chart, figure 1, preferably represents aj 00 as a func- 

 tion of s . A few unmistakably exceptional values of aj 00 are 

 either rejected or replaced by «o 57 , * ne justification of which 

 is shown in the Bulletin. 



The chart shows clearly, I think, that the alloys of platinum 

 may be regarded as a class of materials possessing generic elec- 

 trical properties : for the effect of alloying platinum with small 

 amounts ( < 10 per cent) of any other metal, is a variation of 

 temperature-coefficient in a way which is independent of the 



